No company would give leave that too for holiday of fifteen days immediately on joining. Please learn to have office discipline which include punctuality, regularity in attendance and commitment at work. Sabbatical leave is given to people who worked for years in a company that too for reasons like health, visiting abroad, higher education etc with a condition they would come back and serve the company.
If you went off on unauthorised leave of 15 days after working for a month, most companies would have terminated you long before.
instead, i would suggest you focus on work, work sincerely and prove to them that you are worth keeping as an employeee